1. Field of the Invention
The present invention relates to an apparatus configured to detect an object from a moving image and a method thereof.
2. Description of the Related Art
A technique for detecting an object from an image is discussed in “Rapid Object Detection using Boosted Cascade of Simple Features” in Proceedings of The IEEE Conference on Computer Vision and Pattern Recognition (CVPR'01), for example. In the technique, a sub-window of a predetermined size in an image is scanned and two-class discrimination is performed for determining whether a pattern image which is clipped out from an image in the sub-window is an object. In the discrimination, a large number of weak discriminators are effectively combined based on adaptive boosting (AdaBoost) to form discriminators, so that accuracy in discrimination is enhanced. In another technique, such discriminators are connected in series to form a cascade detector. In further another technique, weak discriminators are each constructed with Haar-like rectangular feature quantities, and the rectangular feature quantities are computed at high speed using an integral image. The cascade detector uses simpler discriminators (for a less amount of calculation) in former stages to remove pattern candidates that do not include an object obviously. In latter stages, the detector uses more complicated discriminators (for a more amount of calculation) having higher identification capability for discriminating the object from the other pattern candidates. In this case, the complicated discrimination process is not necessary for all of the candidates, so that the discrimination can be performed at high speed.
Japanese Patent Application Laid-Open No. 2003-44853 discusses a technique for increasing discrimination speed by removing patterns that do not include an object in former stage. The technique uses a face learning dictionary for identifying a face image and a non-face image and edge images of a target image, extracts partial images that each seems to include a face image from the target image, and determines whether each of the extracted partial images includes the face image by referring to the learning dictionary.
The above described techniques have been developed to process only one image, and do not discuss any approach for efficiently searching for an object from a moving image.
Japanese Patent Application Laid-Open No. 2007-257358 discusses a method for efficiently detecting an object from a moving image by using frames that are close in terms of time and highly correlated to each other. In the method, when a predetermined object is detected in some hierarchy in an object detection process, the object detection process of a next input image is performed on hierarchical images in the same hierarchy which includes the predetermined object.
In the above technique, a detection result is used to control a region to be searched for in a next frame, and the regions without the object at that time are excluded from the searching. Accordingly, the overall regions need to be regularly processed to search for an object that comes into a frame later, or an object that steps out of shade, so that detection of an object cannot perform efficiently.